Inflatable catheter for selective organ heating and cooling and method of using the same

ABSTRACT

A catheter system and method are provided which change the temperature of a fluid, such as blood, by heat transfer. Selective cooling or heating of an organ may be performed by changing the temperature of the blood feeding the organ. The catheter system includes an inlet lumen and an outlet lumen structured and arranged to carry a working fluid having a temperature different from the adjacent blood. The outlet lumen is configured to induce turbulence in the adjacent fluid passing adjacent the outlet lumen.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation-in-part patent application of co-pendingU.S. patent application Ser. No. 09/103,342, filed on Jun. 23, 1998, andentitled “Selective Organ Cooling Catheter and Method of Using theSame”, and of co-pending U.S. patent application Ser. No. 09/047,012,filed on Mar. 24, 1998, and entitled “Improved Selective OrganHypothermia Method and Apparatus”, both of which are incorporated byreference herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The invention relates generally to the modification and controlof the temperature of a selected body organ. More particularly, theinvention relates to a method and intravascular apparatus forcontrolling organ temperature.

[0005] 2. Background Information

[0006] Organs in the human body, such as the brain, kidney and heart,are maintained at a constant temperature of approximately 37° C.Hypothermia can be clinically defined as a core body temperature of 35°C. or less. Hypothermia is sometimes characterized further according toits severity. A body core temperature in the range of 33° C. to 35° C.is described as mild hypothermia. A body temperature of 28° C. to 32° C.is described as moderate hypothermia. A body core temperature in therange of 24° C. to 28° C. is described as severe hypothermia.

[0007] Hypothermia is uniquely effective in reducing brain injury causedby a variety of neurological insults and may eventually play animportant role in emergency brain resuscitation. Experimental evidencehas demonstrated that cerebral cooling improves the patient's outcomeafter global ischemia, focal ischemia, or traumatic brain injury. Forthis reason, hypothermia may be induced in order to reduce the effect ofcertain bodily injuries to the brain as well as other organs.

[0008] Cerebral hypothermia has traditionally been accomplished throughwhole body cooling to create a condition of total body hypothermia inthe range of 20° C. to 30° C. However, the use of total body hypothermiarisks certain deleterious systematic vascular effects. For example,total body hypothermia may cause severe derangement of thecardiovascular system, including low cardiac output, elevated systematicresistance, and ventricular fibrillation. Other side effects includerenal failure, disseminated intravascular coagulation, and electrolytedisturbances. In addition to the undesirable side effects, total bodyhypothermia is difficult to administer.

[0009] Catheters have been developed which are inserted into thebloodstream of the patient in order to induce total body hypothermia.For example, U.S. Pat. No. 3,425,419 to Dato describes a device andtechnique of lowering and raising the temperature of the human body. TheDato reference discloses a technique of inducing moderate hypothermia ina patient using a metallic catheter. The metallic catheter has an innerpassageway through which a fluid, such as water, can be circulated. Thecatheter is inserted through the femoral vein and then through theinferior vena cava as far as the right atrium and the superior venacava. The Dato reference discloses a catheter having an elongatedcylindrical shape and is constructed from stainless steel. By way ofexample, Dato suggests the use of a catheter approximately 70 cm inlength and approximately 6 mm in diameter. However, use of the Datodevice implicates the negative effects of total body hypothermiadescribed above.

[0010] Due to the problems associated with total body hypothermia,attempts have been made to provide more selective cooling. For example,cooling helmets or head gear have been used in an attempt to cool onlythe head rather than the patient's entire body. However, such methodsrely on conductive heat transfer through the skull and into the brain.One drawback of using conductive heat transfer is that the process ofreducing the temperature of the brain is prolonged. Also, it isdifficult to precisely control the temperature of the brain when usingconduction due to the temperature gradient that must be establishedexternally in order to sufficiently lower the internal temperature. Inaddition, when using conduction to cool the brain, the face of thepatient is also subjected to severe hypothermia, increasing discomfortand the likelihood of negative side effects. It is known that profoundcooling of the face can cause similar cardiovascular side effects astotal body cooling. From a practical standpoint, such devices arecumbersome and may make continued treatment of the patient difficult orimpossible.

[0011] Selective organ hypothermia has also been attempted by perfusionof a cold solution such as saline or perflourocarbons. This process iscommonly used to protect the heart during heart surgery and is referredto as cardioplegia. Perfusion of a cold solution has a number ofdrawbacks, including a limited time of administration due to excessivevolume accumulation, cost, and inconvenience of maintaining theperfusate and lack of effectiveness due to the temperature dilution fromthe blood. Temperature dilution by the blood is a particular problem inhigh blood flow organs such as the brain.

[0012] Therefore, there is a need for a practical method and apparatuswhich modifies and controls the temperature of a selected organ but doesnot suffer from the drawbacks of total body hypothermia or coldperfusion.

BRIEF SUMMARY OF THE INVENTION

[0013] The invention provides a method and device to transfer heat to orfrom a selected organ in an efficient manner. The device has a highdegree of lateral flexibility and is collapsible, thereby affording aneasy insertion procedure. The device allows high surface area toincrease heat transfer.

[0014] In one aspect, the invention is directed to a catheter system tochange the temperature of blood by heat transfer to or from a workingfluid. The system includes an inflatable inlet lumen and outlet lumen.The outlet lumen is coupled to the inlet lumen so as to transfer workingfluid between the two. The outlet lumen has a structure when inflated toinduce turbulence in the blood and/or in the working fluid.

[0015] Variations of the system may include one or more of thefollowing. The inlet lumen and the outlet lumen may be made of aflexible material such as latex rubber. The outlet lumen may have astructure to induce turbulence in the working fluid when inflated, suchas a helical shape which may be tapered in a segmented or non-segmentedmanner. The radii of the inlet and outlet lumens may decrease in adistal direction such that the inlet and outlet lumens are tapered wheninflated. A wire may be disposed in the inlet or outlet lumens toprovide shape and strength when deflated.

[0016] The thickness of the outlet lumen, when inflated, may be lessthan about ½mil. The length of the inlet lumen may be between about 5and 30 centimeters. If the outlet lumen has a helical shape, thediameter of the helix may be less than about 8 millimeters wheninflated. The outer diameter of the helix of the outlet lumen, wheninflated, may be between about 2 millimeters and 8 millimeters and maytaper to between about 1 millimeter and 2 millimeters. In segmentedembodiments, a length of a segment may be between about 1 centimeter and10 centimeters. The radii of the inlet and outlet lumens when inflatedmay be between about 0.5 millimeters and 2 millimeters.

[0017] The outlet lumen may further include at least one surface featureand/or interior feature, the surface feature inducing turbulence in thefluid adjacent the outlet lumen and the interior feature inducingturbulence in the working fluid. The surface feature may include one ormore helical turns or spirals formed in the outlet lumen. Adjacent turnsmay employ opposite helicity. Alternatively or in combination, thesurface feature may be a series of staggered protrusions formed in theoutlet lumen.

[0018] The turbulence-inducing outlet lumen may be adapted to induceturbulence when inflated within a free stream of blood when placedwithin an artery. The turbulence intensity may be greater than about0.05. The turbulence-inducing outlet lumen may be adapted to induceturbulence when inflated throughout the period of the cardiac cycle whenplaced within an artery or during at least 20% of the period.

[0019] The system may further include a coaxial supply catheter havingan inner catheter lumen coupled to the inlet lumen and a working fluidsupply configured to dispense the working fluid and having an outputcoupled to the inner catheter lumen. The working fluid supply may beconfigured to produce a pressurized working fluid at a temperature ofbetween about −3° C. and 36° C. and at a pressure below about 5atmospheres of pressure. Higher temperatures may be employed if bloodheating is desired.

[0020] The turbulence-inducing outlet lumen may include a surfacecoating or treatment such as heparin to inhibit clot formation. A stentmay be coupled to the distal end of the inlet lumen. The system may beemployed to cool or heat volumes of tissue rather than blood.

[0021] In embodiments employing a tapered helical outlet lumen, thetaper of the outlet lumen allows the outlet lumen to be placed in anartery having a radius less than the first radius. The outlet lumen maybe tapered in segments. The segments may be separated by joints, thejoints having a radius less than that of either adjacent segment.

[0022] In another aspect, the invention is directed to a method ofchanging the temperature of blood by heat transfer. The method includesinserting an inflatable heat transfer element into an artery or vein andinflating the same by delivering a working fluid to its interior. Thetemperature of the working fluid is generally different from that of theblood. The method further includes inducing turbulence in the workingfluid by passing the working fluid through a turbulence-inducing path,such that turbulence is induced in a substantial portion of a freestream of blood. The inflatable heat transfer element may have aturbulence-inducing structure when inflated.

[0023] In another aspect, the invention is directed towards a method oftreating the brain which includes inserting a flexible heat transferelement into an artery from a distal location and circulating a workingfluid through the flexible heat transfer element to inflate the same andto selectively modify the temperature of an organ without significantlymodifying the temperature of the entire body. The flexible, conductiveheat transfer element preferably absorbs more than about 25, 50 or 75watts of heat. The artery may be the common carotid or a combination ofthe common carotid and the internal carotid.

[0024] In another aspect, the invention is directed towards a method forselectively cooling an organ in the body of a patient which includesintroducing a catheter into a blood vessel supplying the organ, thecatheter having a diameter of 5 mm or less, inducing free streamturbulence in blood flowing over the catheter, and cooling the catheterto remove heat from the blood to cool the organ without substantiallycooling the entire body. In one embodiment, the cooling removes at leastabout 75 watts of heat from the blood. In another embodiment, thecooling removes at least about 100 watts of heat from the blood. Theorgan being cooled may be the human brain.

[0025] The circulating may further include passing the working fluid inthrough an inlet lumen and out through an outlet, coaxial lumen. Theworking fluid may be a liquid at or well below its boiling point, andfurthermore may may be aqueous.

[0026] Advantages of the invention include one or more of the following.The design criteria described above for the heat transfer element: smalldiameter when deflated, large diameter when inflated, high flexibility,and enhanced heat transfer rate through increases in the surface of theheat transfer element and the creation of turbulent flow, facilitatecreation of a heat transfer element which successfully achievesselective organ cooling or heating. Because only a selected organ iscooled, complications associated with total body hypothermia areavoided. Because the blood is cooled intravascularly, or in situ,problems associated with external circulation of the blood areeliminated. Also, only a single puncture and arterial vessel cannulationare required which may be performed at an easily accessible artery suchas the femoral, subclavian, or brachial arteries. By eliminating the useof a cold perfusate, problems associated with excessive fluidaccumulation are avoided. In addition, rapid cooling to a precisetemperature may be achieved. Further, treatment of a patient is notcumbersome and the patient may easily receive continued care during theheat transfer process. The device and method may be easily combined withother devices and techniques to provide aggressive multiple therapies.Other advantages will become clear from the description below.

[0027] The novel features of this invention, as well as the inventionitself, will be best understood from the attached drawings, taken alongwith the following description, in which similar reference charactersrefer to similar parts, and in which:

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0028] The features, objects, and advantages of the invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify corresponding elements throughout.

[0029]FIG. 1 is a schematic diagram of a heat transfer element accordingto an embodiment of the invention.

[0030]FIG. 2 is a side schematic view of an inflatableturbulence-inducing heat transfer element according to an embodiment ofthe invention, as the same is disposed within an artery.

[0031]FIG. 3 illustrates an inflatable turbulence-inducing heat transferelement according to an alternative embodiment of the inventionemploying a surface area enhancing taper and a turbulence-inducingshape.

[0032]FIG. 4 illustrates a tapered joint which may be employed in theembodiment of FIG. 3.

[0033]FIG. 5 illustrates a turbulence-inducing heat transfer elementaccording to a second alternative embodiment of the invention employinga surface area enhancing taper and turbulence-inducing surface features.

[0034]FIG. 6 illustrates a type of turbulence-inducing surface featurewhich may be employed in the heat transfer element of the embodiment ofFIG. 5. In FIG. 6 a spiral feature is shown.

[0035]FIG. 7 illustrates another type of turbulence-inducing surfacefeature which may be employed in the heat transfer element of theembodiment of FIG. 5. In FIG. 7, a series of staggered protrusions areshown.

[0036]FIG. 8 is a transverse cross-sectional view of the heat transferelement of the embodiment of FIG. 7.

[0037]FIG. 9 illustrates a heat transfer element according to a thirdalternative embodiment of the invention employing a surface areaenhancing taper.

[0038]FIG. 10 is a schematic representation of an embodiment of theinvention being used to cool the brain of a patient.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The temperature of a selected organ may be intravascularlyregulated by a heat transfer element placed in the organ's feedingartery to absorb or deliver heat to or from the blood flowing into theorgan. While the device is described with respect to blood flow into anorgan, it is understood that heat transfer within a volume of tissue isanalogous. In the latter case, heat transfer is predominantly byconduction.

[0040] The heat transfer may cause either a cooling or a heating of theselected organ. A heat transfer element that selectively alters thetemperature of an organ should be capable of providing the necessaryheat transfer rate to produce the desired cooling or heating effectwithin the organ to achieve a desired temperature.

[0041] The heat transfer element should be small and flexible enough tofit within the feeding artery while still allowing a sufficient bloodflow to reach the organ in order to avoid ischemic organ damage. Feedingarteries, like the carotid artery, branch off the aorta at variouslevels. Subsidiary arteries continue to branch off these initialbranches. For example, the internal carotid artery branches off thecommon carotid artery near the angle of the jaw. The heat transferelement is typically inserted into a peripheral artery, such as thefemoral artery, using a guide catheter or guide wire, and accesses afeeding artery by initially passing though a series of one or more ofthese branches. Thus, the flexibility and size, e.g., the diameter, ofthe heat transfer element are important characteristics. Thisflexibility is achieved as is described in more detail below.

[0042] These points are illustrated using brain cooling as an example.The common carotid artery supplies blood to the head and brain. Theinternal carotid artery branches off the common carotid artery to supplyblood to the anterior cerebrum. The heat transfer element according tothe principles of the invention may be placed into the common carotidartery or into both the common carotid artery and the internal carotidartery.

[0043] The benefits of hypothermia described above are achieved when thetemperature of the blood flowing to the brain is reduced to between 30°C. and 32° C. A typical brain has a blood flow rate through each carotidartery (right and left) of approximately 250-375 cubic centimeters perminute (cc/min). With this flow rate, calculations show that the heattransfer element should absorb approximately 75-175 watts of heat whenplaced in one of the carotid arteries to induce the desired coolingeffect. Smaller organs may have less blood flow in their respectivesupply arteries and may require less heat transfer, such as about 25watts.

[0044] A device according to an embodiment of the invention foraccomplishing such cooling or heating is shown schematically in FIG. 1,which shows an arterial wall 109 in which a blood flow 100 is passing. Acatheter 101 is disposed within the blood flow 100 to affect the bloodtemperature. Catheter 101 has an inlet lumen 105 for providing a workingfluid 107 and an outlet lumen 103 for draining the working fluid 107.The functions of the respective lumens may of course be opposite to thatstated. A reverse configuration may be particularly advantageous whenblood heating, rather than blood cooling, is the objective.

[0045] Heat transfer in this system is governed by the followingmechanisms:

[0046] (1) convective heat transfer from the blood 100 to the outletlumen 103;

[0047] (2) conduction through the wall of the outlet lumen 103;

[0048] (3) convective heat transfer from the outlet lumen 103 to theworking fluid 107;

[0049] (4) conduction through the working fluid 107;

[0050] (5) convective heat transfer from working fluid 107 in the outletlumen 103 to the inlet lumen 105; and

[0051] (6) conduction through the wall of the inlet lumen 105.

[0052] Once the materials for the lumens and the working fluid arechosen, the conductive heat transfers are solely dependent on thetemperature gradients. Convective heat transfers, by contrast, also relyon the movement of fluid to transfer heat. Forced convection resultswhen the heat transfer surface is in contact with a fluid whose motionis induced (or forced) by a pressure gradient, area variation, or othersuch force. In the case of arterial flow, the beating heart provides anoscillatory pressure gradient to force the motion of the blood incontact with the heat transfer surface. One of the aspects of the deviceuses turbulence to enhance this forced convective heat transfer.

[0053] The rate of convective heat transfer Q is proportional to theproduct of S, the area of the heat transfer element in direct contactwith the fluid, ΔT=T_(b)−T_(s), the temperature differential between thesurface temperature T_(s) of the heat transfer element and the freestream blood temperature T_(b), and {overscore (h_(c))}, the averageconvection heat transfer coefficient over the heat transfer area.{overscore (h_(c))} is sometimes called the “surface coefficient of heattransfer” or the “convection heat transfer coefficient”.

[0054] The magnitude of the heat transfer rate Q to or from the fluidflow can be increased through manipulation of the above threeparameters. Practical constraints limit the value of these parametersand how much they can be manipulated. For example, the internal diameterof the common carotid artery ranges from 6 to 8 mm. Thus, the heattransfer element residing therein may not be much larger than 4 mm indiameter to avoid occluding the vessel. The length of the heat transferelement should also be limited. For placement within the internal andcommon carotid artery, the length of the heat transfer element islimited to about 10 cm. This estimate is based on the length of thecommon carotid artery, which ranges from 8 to 12 cm.

[0055] Consequently, the value of the surface area S is limited by thephysical constraints imposed by the size of the artery into which thedevice is placed. Surface features, such as fins, can be used toincrease the surface area of the heat transfer element, however, thesefeatures alone cannot provide enough surface area enhancement to meetthe required heat transfer rate to effectively cool the brain. Anembodiment of the device described below provides a tapered heattransfer element which employs a large surface area but which mayadvantageously fit into small arteries. As the device is inflatable, thesame may be inserted in relatively small arteries in a deflated state,allowing a minimally invasive entry. When the device is in position, thesame may be inflated, allowing a large surface area and thus an enhancedheat transfer rate.

[0056] One may also attempt to vary the magnitude of the heat transferrate by varying ΔT. The value of ΔT=T_(b)−T_(s) can be varied by varyingthe surface temperature T_(s) of the heat transfer element. Theallowable surface temperature of the heat transfer element is limited bythe characteristics of blood. The blood temperature is fixed at about37° C., and blood freezes at approximately 0° C. When the bloodapproaches freezing, ice emboli may form in the blood which may lodgedownstream, causing serious ischemic injury. Furthermore, reducing thetemperature of the blood also increases its viscosity which results in asmall decrease in the value of {overscore (h_(c))}. Increased viscosityof the blood may further result in an increase in the pressure dropwithin the artery, thus compromising the flow of blood to the brain.Given the above constraints, it is advantageous to limit the surfacetemperature of the heat transfer element to approximately 1° C.-5° C.,thus resulting in a maximum temperature differential between the bloodstream and the heat transfer element of approximately 32° C.-36° C.

[0057] One may also attempt to vary the magnitude of the heat transferrate by varying {overscore (h_(c))}. Fewer constraints are imposed onthe value of the convection heat transfer coefficient {overscore(h_(c))}. The mechanisms by which the value of {overscore (h_(c))} maybe increased are complex. However, one way to increase {overscore(h_(c))} for a fixed mean value of the velocity is to increase the levelof turbulent kinetic energy in the fluid flow.

[0058] The heat transfer rate Q_(no-flow) in the absence of fluid flowis proportional to ΔT, the temperature differential between the surfacetemperature T_(s) of the heat transfer element and the free stream bloodtemperature T_(b) times k, the diffusion constant, and is inverselyproportion to δ, the thickness of the boundary layer.

[0059] The magnitude of the enhancement in heat transfer by fluid flowcan be estimated by taking the ratio of the heat transfer rate withfluid flow to the heat transfer rate in the absence of fluid flowN=Q_(flow)/Q_(no-flow)={overscore (h_(c))}/(k/δ). This ratio is calledthe Nusselt number (“Nu”). For convective heat transfer between bloodand the surface of the heat transfer element, Nusselt numbers of 30-80have been found to be appropriate for selective cooling applications ofvarious organs in the human body. Nusselt numbers are generallydependent on several other numbers: the Reynolds number, the Womersleynumber, and the Prandtl number.

[0060] Stirring-type mechanisms, which abruptly change the direction ofvelocity vectors, may be utilized to induce turbulent kinetic energy andincrease the heat transfer rate. The level of turbulence so created ischaracterized by the turbulence intensity θ. Turbulence intensity θ isdefined as the root mean square of the fluctuating velocity divided bythe mean velocity. Such mechanisms can create high levels of turbulenceintensity in the free stream, thereby increasing the heat transfer rate.This turbulence intensity should ideally be sustained for a significantportion of the cardiac cycle, and should ideally be created throughoutthe free stream and not just in the boundary layer.

[0061] Turbulence does occur for a short period in the cardiac cycleanyway. In particular, the blood flow is turbulent during a smallportion of the descending systolic flow. This portion is less than 20%of the period of the cardiac cycle. If a heat transfer element is placedco-axially inside the artery, the heat transfer rate will be enhancedduring this short interval. For typical of these fluctuations, theturbulence intensity is at least 0.05. In other words, the instantaneousvelocity fluctuations deviate from the mean velocity by at least 5%.Although ideally turbulence is created throughout the entire period ofthe cardiac cycle, the benefits of turbulence are obtained if theturbulence is sustained for 75%, 50% or even as low as 30% or 20% of thecardiac cycle.

[0062] One type of turbulence-inducing heat transfer element which maybe advantageously employed to provide heating or cooling of an organ orvolume is described in co-pending U.S. patent application Ser. No.09/103,342 to Dobak and Lasheras for a “Selective Organ Cooling Catheterand Method of Using the Same,” incorporated by reference above. In thatapplication, the heat transfer element is made of a high thermalconductivity material, such as metal. The metal heat transfer elementprovides a high degree of heat transfer due to its high thermalconductivity. In that application, bellows provided a high degree ofarticulation that compensated for the intrinsic stiffness of the metal.The device size was minimized, e.g., less than 4 mm, to prevent blockageof the blood flowing in the artery.

[0063] On the other hand, the heat transfer element according to anembodiment of the present invention is made of a flexible material, suchas latex rubber. The latex rubber provides a high degree of flexibilitywhich was previously achieved by articulation. The latex rubber furtherallows the heat transfer element to be made collapsible so that whendeflated the same may be easily inserted into an artery. Insertion andlocation may be conveniently made by way of a guide catheter or guidewire. Following insertion and location in the desired artery, the heattransfer element may be inflated for use by a working fluid such assaline, water, perfluorocarbons, or other suitable fluids.

[0064] A heat transfer element made of a flexible material generally hassignificantly less thermal conductivity than a heat transfer elementmade of metal. The device compensates for this by enhancing the surfacearea available for heat transfer. This may be accomplished in two ways:by increasing the cross-sectional size and by increasing the length.Regarding the former, the device may be structured to be large wheninflated, because when deflated the same may still be inserted into anartery. In fact, the device may be as large as the arterial wall, solong as a path for blood flow is allowed, because the flexibility of thedevice tends to prevent damage to the arterial wall even upon contact.Such paths are described below. Regarding the latter, the device may beconfigured to be long. One way to configure a long device is to taperthe same so that the device may fit into distal arteries having reducedradii in a manner described below. The device further compensates forthe reduced thermal conductivity by reducing the thickness of the heattransfer element wall.

[0065] Embodiments of the device use a heat transfer element design thatproduces a high level of turbulence in the free stream of the blood andin the working fluid. One embodiment of the invention forces a helicalmotion on the working fluid and imposes a helical barrier in the blood,causing turbulence. In an alternative embodiment, the helical barrier istapered. In a second alternative embodiment, a tapered inflatable heattransfer element has surface features to cause turbulence. As oneexample, the surface features may have a spiral shape. In anotherexample, the surface features may be staggered protrusions. In all ofthese embodiments, the design forces a high level of turbulence in thefree stream of the blood by causing the blood to navigate a tortuouspath while passing through the artery. This tortuous path causes theblood to undergo violent accelerations resulting in turbulence.

[0066] In a third alternative embodiment of the invention, a taper of aninflatable heat transfer element provides enough additional surface areaper se to cause sufficient heat transfer. In all of the embodiments, theinflation is performed by the working fluid, such as water or saline.

[0067] Referring to FIG. 2, a side view is shown of a first embodimentof a heat transfer element 14 according to an embodiment of theinvention. The heat transfer element 14 is formed by an inlet lumen 22and an outlet lumen 20. In this embodiment, the outlet lumen 20 isformed in a helix shape surrounding the inlet lumen 22 that is formed ina pipe shape. The names of the lumens are of course not limiting. Itwill be clear to one skilled in the art that the inlet lumen 22 mayserve as an outlet and the outlet lumen 20 may serve as an inlet. Itwill also be clear that the heat transfer element is capable of bothheating (by delivering heat to) and cooling (by removing heat from) adesired area.

[0068] The heat transfer element 14 is rigid but flexible so as to beinsertable in an appropriate vessel by use of a guide catheter.Alternatively, the heat transfer element may employ a device forthreading a guide wire therethrough to assist placement within anartery. The heat transfer element 14 has an inflated length of L, ahelical diameter of D_(c), a tubal diameter of d, and a helical angle ofα. For example, D_(c) may be about 3.3 mm and d may be about 0.9 mm to 1mm. Of course, the tubal diameter d need not be constant. For example,the diameter of the inlet lumen 22 may differ from that of the outletlumen 14.

[0069] The shape of the outlet lumen 20 in FIG. 2 is helical. Thishelical shape presents a cylindrical obstacle, in cross-section, to theflow of blood. Such obstacles tend to create turbulence in the freestream of blood. In particular, the form of turbulence is the creationof von Karman vortices in the wake of the flow of blood, downstream ofthe cylindrical obstacles.

[0070] Typical inflatable materials are not highly thermally conductive.They are much less conductive than the metallic heat transfer elementdisclosed in the patent application incorporated by reference above. Thedifference in conductivity is compensated for in at least two ways inthe present device. The material is made thinner and the heat transferelement is afforded a larger surface area. Regarding the former, thethickness may be less than about ½mil for adequate cooling.

[0071] Thin inflatable materials, particularly those with large surfaceareas, may require a structure, such as a wire, within their interiorsto maintain their approximate uninflated positions so that uponinflation, the proper form is achieved. Thus, a wire structure 67 isshown in FIG. 2 which may be advantageously disposed within theinflatable material to perform such a function.

[0072] Another consideration is the angle α of the helix. Angle α shouldbe determined to optimize the helical motion of the blood around thelumens 20 and 22, enhancing heat transfer. Of course, angle α shouldalso be determined to optimize the helical motion of the working fluidwithin the lumens 20 and 22. The helical motion of the working fluidwithin the lumens 20 and 22 increases the turbulence in the workingfluid by creating secondary motions. In particular, helical motion of afluid in a pipe induces two counter-rotating secondary flows.

[0073] An enhancement of {overscore (h_(c))} would be obtained in thissystem, and this enhancement may be described by a Nusselt number Nu ofup to about 10 or even more.

[0074] The above discussion describes one embodiment of a heat transferelement. An alternative embodiment of the device, shown in a side viewin FIG. 3, illustrates a heat transfer element 41 with a surface areaenhancement. Increasing the surface area of the inflatable materialenhances heat transfer. The heat transfer element 14 includes a seriesof coils or helices of different coil diameters and tubal diameters. Itis not strictly necessary that the tubal diameters differ, but it islikely that commercially realizable systems will have differing tubaldiameters. The heat transfer element 14 may taper either continuously orsegmentally.

[0075] This alternative embodiment enhances surface area in two ways.First, the use of smaller diameter lumens enhances the overallsurface-to-volume ratio. Second, the use of progressively smaller (i.e.,tapered) lumens allows a distal end 69 to be inserted further into anartery than would be possible with the embodiment of FIG. 2.

[0076] In the embodiment of FIG. 3, a first coil segment 42 is shownhaving length L₁ and diameter D_(C1). The first coil segment 42 isformed of an inlet lumen 51 having diameter d₁ and an outlet lumen 53having diameter d₁′. In the first coil segment, as well as the others,the outlet lumen need not immediately drain the inlet lumen. In FIG. 3,the inlet lumen for each segment feeds the inlet lumen of the succeedingsegment except for an inlet lumen adjacent a distal end 69 of the heattransfer element 41 which directly feeds its corresponding outlet lumen.

[0077] A separate embodiment may also be constructed in which the inletlumens each provide working fluid to their corresponding outlet lumens.In this embodiment, either a separate lumen needs to be provided todrain each outlet lumen or each outlet lumen drains into the adjacentoutlet lumen. This embodiment has the advantage that an oppositehelicity may be accorded each successive segment. The oppositehelicities in turn enhance the turbulence of the working fluid flowingpast them.

[0078] A second coil segment 44 is shown having length L₂ and diameterD_(C2). The second coil segment 44 is formed of an inlet lumen 55 havingdiameter d₂ and an outlet lumen 57 having diameter d₂′. A third coilsegment 46 is shown having length L₃ and diameter D_(C3). The third coilsegment 46 is formed of an inlet lumen 59 having diameter d₃ and anoutlet lumen 61 having diameter d₃′. Likewise, a fourth coil segment 48is shown having length L₄ and diameter D_(C4). The fourth coil segment48 is formed of an inlet lumen 63 having diameter d₄ and an outlet lumen65 having diameter d₄′. The diameters of the lumens, especially that ofthe lumen located at or near distal end 69, should be large enough tonot restrict the flow of the working fluid within them. Of course, anynumber of lumens may be provided depending on the requirements of theuser.

[0079]FIG. 4 shows the connection between two adjacent inlet lumens 51and 55. A joint 167 is shown coupling the two lumens. The constructionof the joint may be by way of variations in stress, hardening, etc.

[0080] An advantage to this alternative embodiment arises from thesmaller diameters of the distal segments. The heat transfer element ofFIG. 3 may be placed in smaller workspaces than the heat transferelement of FIG. 2. For example, a treatment for brain trauma may includeplacement of a cooling device in the internal carotid artery of apatient. As noted above, the common carotid artery feeds the internalcarotid artery. In some patients, the heat transfer element of FIG. 2may not fit in the internal carotid artery. Similarly, the first coilsegment of the heat transfer element in FIG. 3 may not easily fit in theinternal carotid artery, although the second, third, and fourth segmentsmay fit. Thus, in the embodiment of FIG. 3, the first coil segment mayremain in the common carotid artery while the segments of smallerdiameter (the second, third, and fourth) may be placed in the internalcarotid artery. In fact, in this embodiment, D_(C1) may be large, suchas 5-6 mm. The overall length of the heat transfer element 41 may be,e.g., about 20 to 25 cm.

[0081] An additional advantage was mentioned above. The surface area ofthe alternative embodiment of FIG. 3 may be substantially larger thanthat of the embodiment of FIG. 2, resulting in significantly enhancedheat transfer. For example, the enhancement in surface area may besubstantial, such as up to or even more than three times compared to thesurface area of the device of the application incorporated by referenceabove. An additional advantage of both embodiments is that the helicalrounded shape allows atraumatic insertion into cylindrical cavities suchas, e.g., arteries.

[0082] The embodiment of FIG. 3 may result in an Nu from 1 up to about50.

[0083]FIG. 5 shows a second alternative embodiment of the deviceemploying surface features rather than overall shape to induceturbulence. In particular, FIG. 5 shows a heat transfer element 201having an inlet lumen (not shown) and an outlet inflatable lumen 220having four segments 203, 205, 207, and 221. Segment 203 is adjacent aproximal end 211 and segment 221 is adjacent a distal end 213. Thesegments are arranged having reducing radii in the direction of theproximal end to the distal end. In a manner similar to that of theembodiment of FIG. 3, the feature of reducing radii allows insertion ofthe heat transfer element into small work places such as small arteries.

[0084] Heat transfer element 201 has a number of surface features 215disposed thereon. The surface features 215 may be constructed with,e.g., various hardening treatments applied to the heat transfer element201, or alternatively by injection molding. The hardening treatments mayresult in a wavy or corrugated surface to the exterior of heat transferelement 201. The hardening treatments may further result in a wavy orcorrugated surface to the interior of heat transfer element 201. FIG. 6shows a variation of this embodiment, in which a fabrication process isused which results in a spiral or helical shape to the surface features.

[0085] The embodiment of FIG. 5 may result in an Nu of about 1 to 50.

[0086] In another variation of this embodiment, shown in FIG. 7, a heattransfer element 150 employs a plurality of protrusions 154 on outletlumen 152 which surrounds an inlet lumen 158. In particular, FIG. 7 is acut-away perspective view of an alternative embodiment of a heattransfer element 150. A working fluid is circulated through an inletlumen 156 to a distal tip of the heat transfer element 150 therebyinflating the heat transfer element 150. The working fluid thentraverses an outlet coaxial lumen 160 in order to transfer heat from theexterior surface 152 of the heat transfer element 150. The insidestructure of the heat transfer element 150 is similar to the exteriorstructure in order to induce turbulent flow of the working fluid.

[0087] An external surface 152 of the inflatable heat transfer element150 is covered with a series of staggered protrusions 154. The staggerednature of the protrusions 154 is readily seen with reference to FIG. 8which is a transverse cross-sectional view of an inflated heat transferelement taken along the line 8-8 in FIG. 7. In order to induce freestream turbulence, the height, d_(p), of the staggered protrusions 154is greater than the thickness of the boundary layer which would developif a smooth heat transfer element had been introduced into the bloodstream. As the blood flows along the external surface 152, it collideswith one of the staggered protrusions 154 and a turbulent flow iscreated. As the blood divides and swirls along side of the firststaggered protrusion 154, it collides with another staggered protrusion154 within its path preventing the re-lamination of the flow andcreating yet more turbulence. In this way, the velocity vectors arerandomized and free stream turbulence is created. As is the case withthe other embodiments, this geometry also induces a turbulent effect onthe internal coolant flow.

[0088] The embodiment of FIG. 7 may result in an Nu of about 1 to 50.

[0089] Of course, other surface features may also be used which resultin turbulence in fluids flowing past them. These include spirals,helices, protrusions, various polygonal bodies, pyramids, tetrahedrons,wedges, etc.

[0090] In some situations, an enhanced surface area alone, without thecreation of additional turbulence, may result in sufficient heattransfer to cool the blood. Referring to FIG. 9, a heat transfer element302 is shown having an inlet lumen 304 and an outlet lumen 306. Theinlet lumen 304 provides a working fluid to the heat transfer element302 and outlet lumen 306 drains the working fluid from the same. Thefunctions may, of course, be reversed. The heat transfer element 302 isfurther divided into five segments, although more or less may beprovided as dictated by requirements of the user. The five segments inFIG. 9 are denoted segments 308, 310, 312, 314, and 316. In FIG. 9, thesegment 308 has a first and largest radius R₁, followed by correspondingradii for segments 310, 312, 314, and 316. Segment 316 has a second andsmallest radius. The length of the segment 308 is L₁, followed bycorresponding lengths for segments 310, 312, 314, and 316.

[0091] A purely tapered (nonsegmented) form may replace the taperedsegmental form, but the former may be more difficult to manufacture. Ineither case, the tapered form allows the heat transfer element 302 to bedisposed in small arteries, i.e., arteries with radii smaller than R₁. Asufficient surface area is thus afforded even in very small arteries toprovide the required heat transfer.

[0092] The surface area and thus the size of the device should besubstantial to provide the necessary heat transfer. Example dimensionsfor a three-segmented tapered form may be as follows: L₁=10 cm, R₁=2.5mm; L₂=10 cm, R₂=1.65 mm, L₃=5 cm, R₃= 1 mm. Such a heat transferelement would have an overall length of 25 cm and a surface area of3×10⁻⁴ m².

[0093] The embodiment of FIG. 9 results in an enhancement of the heattransfer rate of up to about 300% due to the increased surface area Salone.

[0094] A variation of the embodiment of FIG. 9 includes placing at leastone turbulence-inducing surface feature within the interior of theoutlet lumen 306. This surface feature may induce turbulence in theworking fluid, thereby increasing the convective heat transfer rate inthe manner described above.

[0095] Another variation of the embodiment of FIG. 9 involves reducingthe joint diameter between segments (not shown). For example, theinflatable material may be formed such that joints 318, 320, 322, and324 have a diameter only slightly greater than that of the inlet lumen304. In other words, the heat transfer element 302 has a tapered“sausage” shape.

[0096] In all of the embodiments, the inflatable material may be formedfrom seamless and nonporous materials which are therefore impermeable togas. Impermeability can be particularly important depending on the typeof working fluid which is cycled through the heat transfer element. Forexample, the inflatable material may be latex or other such rubbermaterials, or alternatively of any other material with similarproperties under inflation. The flexible material allows the heattransfer element to bend, extend and compress so that it is more readilyable to navigate through tiny blood vessels. The material also providesfor axial compression of the heat transfer element which can limit thetrauma when the distal end of the heat transfer element 14 abuts a bloodvessel wall. The material should be chosen to tolerate temperatures inthe range of −1° C. to 37° C., or even higher in the case of bloodheating, without a loss of performance.

[0097] It may be desirable to treat the surface of the heat transferelement to avoid clot formation because the heat transfer element maydwell within the blood vessel for extended periods of time, such as24-48 hours or even longer. One means by which to prevent thrombusformation is to bind an antithrombogenic agent to the surface of theheat transfer element. For example, heparin is known to inhibit clotformation and is also known to be useful as a biocoating.

[0098] Referring back to FIG. 2, an embodiment of the method of theinvention will be described. A description with reference to theembodiment of FIG. 3 is analogous. A guide catheter or wire may bedisposed up to or near the area to be cooled or heated. The case of aguide catheter will be discussed here. The heat transfer element may befed through the guide catheter to the area. Alternatively, the heattransfer element may form a portion of the guide catheter. A portion ofthe interior of the guide catheter may form, e.g., the return lumen forthe working fluid. In any case, the movement of the heat transferelement is made significantly more convenient by the flexibility of theheat transfer element as has been described above.

[0099] Once the heat transfer element 14 is in place, a working fluidsuch as saline or other aqueous solution may be circulated through theheat transfer element 14 to inflate the same. Fluid flows from a supplycatheter into the inlet lumen 22. At the distal end 26 of the heattransfer element 14, the working fluid exits the inlet lumen 22 andenters the outlet lumen 20.

[0100] In the case of the embodiment of FIG. 5, for which thedescription of FIG. 7 is analogous, the working fluid exits the inletlumen and enters an outlet inflatable lumen 220 having segments 203,205, 207, and 221. As the working fluid flows through the outlet lumen220, heat is transferred from the exterior surface of the heat transferelement 201 to the working fluid. The temperature of the externalsurface may reach very close to the temperature of the working fluidbecause the heat transfer element 201 is constructed from very thinmaterial.

[0101] The working fluids that may be employed in the device includewater, saline or other fluids which remain liquid at the temperaturesused. Other coolants, such as freon, undergo nucleated boiling and maycreate turbulence through a different mechanism. Saline is a safecoolant because it is non-toxic and leakage of saline does not result ina gas embolism which may occur with the use of boiling refrigerants.

[0102] By enhancing turbulence in the coolant, the coolant can bedelivered to the heat transfer element at a warmer temperature and stillachieve the necessary heat transfer rate. In particular, the enhancedheat transfer characteristics of the internal structure allow theworking fluid to be delivered to the heat transfer element at lower flowrates and lower pressures. This is advantageous because high pressuresmay stiffen the heat transfer element and cause the same to push againstthe wall of the vessel, thereby shielding part of the heat transfer unitfrom the blood. Such pressures are unlikely to damage the walls of thevessel because of the increased flexibility of the inflated device. Theincreased heat transfer characteristics allow the pressure of theworking fluid to be delivered at pressures as low as 5 atmospheres, 3atmospheres, 2 atmospheres or even less than 1 atmosphere.

[0103] In a preferred embodiment, the heat transfer element creates aturbulence intensity greater than 0.05 in order to create the desiredlevel of turbulence in the entire blood stream during the whole cardiaccycle. The turbulence intensity may be greater than 0.055, 0.06, 0.07 orup to 0.10 or 0.20 or even greater.

[0104]FIG. 10 is a schematic representation of the device being used tocool the brain of a patient. The selective organ hypothermia apparatusincludes a working fluid supply 16, preferably supplying a chilledliquid such as water, alcohol or a halogenated hydrocarbon, a supplycatheter 12 and the heat transfer element 15. The heat transfer element15 may have the form, e.g., of any of the embodiments above or ofsimilar such heat transfer elements. The supply catheter 12 has acoaxial construction. An inlet lumen within the supply catheter 12receives coolant from the working fluid supply 16. The coolant travelsthe length of the supply catheter 12 to the heat transfer element 15which serves as the cooling tip of the catheter. At the distal end ofthe heat transfer element 15, the coolant exits the insulated interiorlumen and traverses the length of the heat transfer element 15 in orderto decrease the temperature of the heat transfer element 15. The coolantthen traverses an outlet lumen of the supply catheter 12, which may havea helical or other shape as described above. The supply catheter 12 is aflexible catheter having a diameter sufficiently small to allow itsdistal end to be inserted percutaneously into an accessible artery suchas the femoral artery of a patient. The supply catheter 12 issufficiently long to allow the heat transfer element 15 to be passedthrough the vascular system of the patient and placed in the internalcarotid artery or other small artery. If the heat transfer element 15employs tapering as in some of the embodiments described above, the samemay be placed in very small arteries without damage to the arterialwalls.

[0105] The heat transfer element can absorb or provide over 75 watts ofheat to the blood stream and may absorb or provide as much as 100 watts,150 watts, 170 watts or more. For example, a heat transfer element witha diameter of 4 mm and a length of approximately 10 cm, using ordinarysaline solution chilled so that the surface temperature of the heattransfer element is approximately 5° C. and pressurized at 2atmospheres, can absorb about 150 watts of energy from the bloodstream.Smaller geometry heat transfer elements may be developed for use withsmaller organs which provide 60 watts, 50 watts, 25 watts or less ofheat transfer.

[0106] The practice of the invention is illustrated in the followingnon-limiting example.

EXEMPLARY PROCEDURE

[0107] 1. The patient is initially assessed, resuscitated, andstabilized.

[0108] 2. The procedure is carried out in an angiography suite orsurgical suite equipped with fluoroscopy.

[0109] 3. Because the catheter is placed into the common carotid artery,it is important to determine the presence of stenotic atheromatouslesions. A carotid duplex (Doppler/ultrasound) scan can quickly andnon-invasively make this determination. The ideal location for placementof the catheter is in the left carotid. Thus, the same may be scannedfirst. If disease is present, then the right carotid artery can beassessed. This test can be used to detect the presence of proximalcommon carotid lesions by observing the slope of the systolic upstrokeand the shape of the pulsation. Although these lesions are rare, theycould inhibit the placement of the catheter. Examination of the peakblood flow velocities in the internal carotid can determine the presenceof internal carotid artery lesions. Although the catheter is placedproximally to such lesions, the catheter may exacerbate the compromisedblood flow created by these lesions. Peak systolic velocities greaterthat 130 cm/sec and peak diastolic velocities>100 cm/sec in the internalcarotid indicate the presence of at least 70% stenosis. Stenosis of 70%or more may warrant the placement of a stent to open up the internalartery diameter.

[0110] 4. Ultrasound can also be used to determine the vessel diameterand the blood flow. A catheter with an appropriately-sized heat transferelement could be selected.

[0111] 5. After assessment of the arteries, the patient's inguinalregion is sterilely prepped and infiltrated with lidocaine.

[0112] 6. The femoral artery is cannulated and a guide wire may beinserted to the desired carotid artery. Placement of the guide wire isconfirmed with fluoroscopy.

[0113] 7. An angiographic catheter can be fed over the wire and contrastmedia injected into the artery to further assess the anatomy of thecarotid.

[0114] 8. Alternatively, the femoral artery is cannulated and a 10-12.5french (f) introducer sheath is placed.

[0115] 9. A guide catheter may be placed into the desired common carotidartery. If a guide catheter is placed, it can be used to delivercontrast media directly to further assess carotid anatomy.

[0116] 10. The 10 f-12 f (3.3-4.0 mm) (approximate) heat transfer deviceis then prepared.

[0117] 11. The heat transfer device and supply catheter are placed intothe carotid artery via the guiding catheter or over the guidewire.Placement is confirmed with fluoroscopy. This placement is convenientlymade in part because of the flexibility of the heat transfer element.

[0118] 12. Alternatively, the catheter tip is shaped (angled or curvedapproximately 45 degrees), and the catheter shaft has sufficientpushability and torqueability to be placed in the carotid without theaid of a guide wire or guide catheter. Such pushability andtorqueability may be achieved with the use of a wire placed within thecatheter shaft and heat transfer element.

[0119] 13. If cooling is desired, the catheter according to theinvention is connected to a pump circuit also filled with saline andfree from air bubbles. The pump circuit has a heat exchange section thatis immersed into a water bath and tubing that is connected to aperistaltic pump. The water bath is chilled to approximately 0° C.

[0120] 14. Cooling is initiated by starting the pump mechanism. Thesaline within the cooling catheter is circulated at 5 cc/sec. The salinetravels through the heat exchanger in the chilled water bath and iscooled to approximately 1° C.

[0121] 15. The saline subsequently enters the cooling catheter where itis delivered to the heat transfer element. The saline is warmed toapproximately 5-7° C. as it travels along the inlet lumen of thecatheter shaft to the end of the heat transfer element.

[0122] 16. The saline then flows back through the heat transfer elementin contact with the outlet lumen. The saline is further warmed in theheat transfer element to 12-15° C., and in the process, heat is absorbedfrom the blood, cooling the blood to 30° C. to 32° C.

[0123] 17. The chilled blood then chills the brain. 15-30 minutes may berequired to cool the brain to 30 to 32° C.

[0124] 18. The warmed saline travels back down the outlet lumen of thecatheter shaft and back to the chilled water bath where it is cooled to1° C.

[0125] 19. The pressure drops along the length of the circuit areestimated to be 2-3 atmospheres.

[0126] 20. The cooling can be adjusted by increasing or decreasing theflow rate of the saline. Monitoring the temperature drop of the salinealong the heat transfer element will allow the flow to be adjusted tomaintain the desired cooling effect.

[0127] 21. The catheter may be left in place to provide cooling for 12to 24 hours.

[0128] 22. If desired, warm saline can be circulated to promote warmingof the brain at the end of the therapeutic cooling period.

[0129] In addition, in some applications, it may be advantageous toattach a stent to the distal end of the heat transfer element. The stentmay be used to open arteries partially obstructed by atheromatousdisease prior to initiation of heat transfer. Further, the device may beused to deliver drugs such as blood clot dissolving compounds (e.g.,tissue plasminogen activator (“tPA”), urokinase, pro-urokinase,streptokinase, etc.) or neuroprotective agents (e.g., selectiveneurotransmitter inhibitors). In addition to therapeutic uses, thedevice may be used to destroy tissue such as through cryosurgery.

[0130] While the particular invention as herein shown and disclosed indetail is fully capable of obtaining the objects and providing theadvantages hereinbefore stated, it is to be understood that thisdisclosure is merely illustrative of the presently preferred embodimentsof the invention and that no limitations are intended other than asdescribed in the appended claims.

We claim:
 1. A catheter system to change the temperature of blood byheat transfer to or from a working fluid, comprising: an inlet lumen;and and an outlet lumen, the outlet lumen coupled to the inlet lumen soas to transfer the working fluid between the two, the outlet lumenhaving a structure when inflated to induce turbulence in the blood or inthe working fluid.
 2. The catheter system of claim 1 , wherein the inletlumen and the outlet lumen are made of a flexible material.
 3. Thecatheter system of claim 2 , wherein the flexible material is rubber. 4.The catheter system of claim 3 , wherein the flexible material is latexrubber.
 5. The catheter system of claim 1 , wherein the outlet lumen hasa structure to induce turbulence in the working fluid.
 6. The cathetersystem of claim 5 , wherein the outlet lumen has the shape of a helixwhen inflated.
 7. The catheter system of claim 6 , wherein the helixshape of the outlet lumen is tapered when inflated.
 8. The cathetersystem of claim 7 , wherein the helix shape of the outlet lumen issegmentally tapered when inflated.
 9. The catheter system of claim 8 ,wherein a radius of the inlet lumen decreases such that the inlet lumenis tapered when inflated.
 10. The catheter system of claim 8 , wherein aradius of the outlet lumen decreases such that the outlet lumen istapered when inflated.
 11. The catheter system of claim 1 , furthercomprising a wire disposed within one of at least the inlet lumen or theoutlet lumen.
 12. The catheter system of claim 1 , wherein the thicknessof the outlet lumen when inflated is less than about ½mil.
 13. Thecatheter system of claim 1 , wherein a length of the inlet lumen isbetween about 5 and 30 centimeters.
 14. The catheter system of claim 6 ,wherein a diameter of the helix of the outlet lumen is less than about 8millimeters when inflated.
 15. The catheter system of claim 7 , whereinthe outer diameter of the helix of the outlet lumen, when inflated, isbetween about 2 millimeters and 8 millimeters and tapers to betweenabout 1 millimeter and 2 millimeters.
 16. The catheter system of claim 8, wherein a length of a segment is between about 1 centimeter and 10centimeters.
 17. The catheter system of claim 1 , wherein the radii ofthe inlet and outlet lumens when inflated are between about 0.5millimeters and 2 millimeters.
 18. The catheter system of claim 1 ,wherein the outlet lumen further comprises at least one surface feature,the surface feature inducing turbulence in the fluid adjacent the outletlumen.
 19. The catheter system of claim 18 , wherein the outlet lumenfurther comprises at least one interior feature, the interior featureinducing turbulence in the working fluid.
 20. The catheter system ofclaim 18 , wherein the surface feature is a series of helical turnsformed in the outlet lumen.
 21. The catheter system of claim 20 ,wherein each pair of adjacent turns in the series of helical turns hasopposite helicity.
 22. The catheter system of claim 18 , wherein thesurface feature is a helical shape formed in the outlet lumen.
 23. Thecatheter system of claim 18 , wherein the surface feature is a series ofprotrusions formed in the outlet lumen.
 24. The catheter system of claim1 , wherein the turbulence-inducing outlet lumen is adapted to induceturbulence when inflated within a free stream of blood flow when placedwithin an artery.
 25. The catheter system of claim 24 , wherein theturbulence-inducing outlet lumen is adapted to induce a turbulenceintensity when inflated within a free stream blood flow which is greaterthan 0.05.
 26. The catheter system of claim 24 , wherein theturbulence-inducing exterior surface is adapted to induce turbulencewhen inflated during at least 20% of the period of the cardiac cyclewhen placed within an artery.
 27. The catheter system of claim 26 ,wherein the turbulence-inducing outlet lumen is adapted to induceturbulence when inflated throughout the period of the cardiac cycle whenplaced within an artery.
 28. The catheter system of claim 1 , furthercomprising: a coaxial supply catheter having an inner catheter lumencoupled to the inlet lumen; and a working fluid supply configured todispense the working fluid and having an output coupled to the innercatheter lumen.
 29. The catheter system of claim 28 , wherein theworking fluid supply is configured to produce a pressurized workingfluid at a temperature of between about −3° C. and 36° C. and at apressure below about 5 atmospheres of pressure.
 30. The catheter systemof claim 1 , wherein the turbulence-inducing outlet lumen includes asurface coating or treatment to inhibit clot formation.
 31. The cathetersystem of claim 30 , wherein the surface coating or treatment includesheparin.
 32. The catheter system of claim 1 , further comprising a stentcoupled to the distal end of the inlet lumen.
 33. A catheter system tochange the temperature of blood by heat transfer to or from a workingfluid, comprising: an inlet lumen; and an outlet lumen tapered wheninflated from a first radius to a second radius, the outlet lumencoupled to the inlet lumen so as to transfer the working fluid betweenthe two, such that the taper of the outlet lumen allows the outlet lumento be placed in an artery having a radius less than the first radius.34. A catheter system to change the temperature of blood by heattransfer to or from a working fluid, comprising: an inlet lumen; and anoutlet lumen segmentally tapered when inflated from a first radius to asecond radius, the outlet lumen coupled to the inlet lumen so as totransfer the working fluid between the two, such that adjacent segmentsof the outlet lumen are separated by joints, the joints having a radiusless than that of either adjacent segment, and such that the taper ofthe outlet lumen when inflated allows the outlet lumen to be placed inan artery having a radius less than the first radius.
 35. A cathetersystem to cool the temperature of blood by heat transfer to a workingfluid, comprising: a substantially straight inlet lumen to deliver aworking fluid; and an outlet lumen that when inflated substantiallyhelically surrounds the inlet lumen to remove the working fluid, thehelical shape of the outlet lumen to induce turbulence in the workingfluid and in the blood; such that the helical shape of the outlet lumenis sufficient to induce a turbulence intensity in the blood of greaterthan about 0.05.
 36. A catheter system to cool the temperature of bloodby heat transfer to a working fluid, comprising: a segmentally taperedand substantially straight inlet lumen to deliver a working fluid; andan outlet lumen, the outlet lumen segmentally tapered when inflated andhelically surrounding the inlet lumen to remove the working fluid, thehelical and segmentally tapered shape of the outlet lumen to induceturbulence in the working fluid and in the blood; such that the shape ofthe outlet lumen is sufficient to induce a turbulence intensity in theblood of greater than about 0.05.
 37. A medical catheter system to coolthe temperature of blood by heat transfer to a working fluid,comprising: a substantially straight inflatable inlet lumen to deliver aworking fluid; and a tapered inflatable outlet lumen substantiallysurrounding the inlet lumen to remove the working fluid, an externalsurface of the outlet lumen having surface features to induce turbulencein the working fluid and in the blood; such that the surface featuresare sufficient to induce a turbulence intensity in the blood of greaterthan about 0.05.
 38. A medical catheter system to cool the temperatureof blood by heat transfer to a working fluid, comprising: asubstantially straight inflatable inlet lumen to deliver a workingfluid; and a tapered inflatable outlet lumen substantially surroundingthe inlet lumen to remove the working fluid, an external surface of theoutlet lumen having a spiral formed thereon to induce turbulence in theworking fluid and in the blood; such that the spiral surface feature issufficient to induce a turbulence intensity in the blood of greater thanabout 0.05.
 39. A medical catheter system to cool the temperature ofblood by heat transfer to a working fluid, comprising: a substantiallystraight inflatable inlet lumen to deliver a working fluid; and atapered inflatable outlet lumen substantially surrounding the inletlumen to remove the working fluid, an external surface of the outletlumen having staggered protrusions formed thereon to induce turbulencein the working fluid and in the blood; such that the staggeredprotrusions are sufficient to induce a turbulence intensity in the bloodof greater than about 0.05.
 40. A catheter method of changing thetemperature of blood by heat transfer, comprising: inserting aninflatable heat transfer element into an artery or vein; inflating theinflatable heat transfer element by delivering a working fluid to theinflatable heat transfer element, the temperature of the working fluiddifferent from that of the blood; and inducing turbulence in the workingfluid by passing the working fluid through a turbulence-inducing path,such that turbulence is induced in a substantial portion of a freestream of blood.
 41. A catheter method of changing the temperature ofblood by heat transfer, comprising: inserting an inflatable heattransfer element into a flow of blood in an artery or vein; andinflating the inflatable heat transfer element by delivering a workingfluid having a temperature different than the blood temperature to theinflatable heat transfer element, the inflatable heat transfer elementhaving a turbulence-inducing structure when inflated, such thatturbulence is induced in a substantial portion of a free stream ofblood.
 42. The method of claim 41 , further comprising delivering theworking fluid at a temperature of between about −3° C. and 36° C. 43.The method of claim 41 , further comprising delivering the working fluidat a pressure of less than about 5 atmospheres.
 44. The method of claim43 , further comprising delivering the working fluid at a pressure ofbetween about 1 and 5 atmospheres.
 45. The method of claim 41 , furthercomprising absorbing more than about 75 watts of heat from the blood.46. The method of claim 41 , further comprising inducing bloodturbulence with a turbulence intensity greater than about 0.05 withinthe carotid artery.
 47. The method of claim 41 , wherein the inflatingfurther comprises passing the working fluid through a helical-shapedstructure.
 48. The method of claim 41 , further comprising inducingblood turbulence in greater than 20% of the period of the cardiac cyclewithin the carotid artery.
 49. The method of claim 48 , furthercomprising inducing blood turbulence throughout the period of thecardiac cycle within the carotid artery.
 50. A method for selectivelycooling an organ in a body of a patient, comprising: introducing acatheter having an inflatable heat transfer element into a blood vesselsupplying the organ; inflating the heat transfer element; and inducingfree stream turbulence in blood flowing over the heat transfer element;such that heat is removed from the blood to cool the organ withoutsubstantially cooling the entire body.
 51. A catheter system to changethe temperature of an adjacent material by heat transfer to or from aworking fluid, comprising: an inlet lumen; and an outlet lumen, theoutlet lumen coupled to the inlet lumen so as to transfer the workingfluid between the two, the outlet lumen having a structure to induceturbulence in the working fluid.